1. Field of the Invention
The invention in general relates to capacitors, and more particularly to a solid dielectric capacitor and method of stabilizing it prior to its use in an electric circuit.
2. Description of Related Art
A capacitor is an electrical element which includes two electrodes separated by a dielectric which may be a gas, a liquid or a solid material. Many advanced electrical and electronic systems require low loss capacitors with higher performance in terms of capacitance, energy and power densities and operating temperature. One class of capacitors in use in such systems utilizes a solid dielectric in the form of a polymer.
Improved polymer dielectrics result in a capacitor which can operate at a temperature of less than 300.degree. C. For example, a mica-silicone capacitor is commercially available with a maximum operating temperature of around 260.degree. C., an operating voltage stress value of approximately 25 volts per micron thickness of dielectric material (V/.mu.m), and having an energy density of 0.014 J/cm.sup.3. Most polymer film capacitors, however, generally operate below 100.degree. C. at 100V/.mu.m, with an energy density of approximately 0.15 J/cm.sup.3. Energy discharge polymer film capacitors can operate with short lives at 400 V/.mu.m with an energy density of around 2 J/cm.sup.3.
Ceramics can also be used as high temperature capacitor dielectrics in view of their thermal capability of remaining stable at temperatures greater than 400.degree. C. In addition, the dielectric constant of various ceramics can extend into the thousands, affording them high energy density, whereas that of polymers do not exceed about 20.
Present ceramic capacitor dielectrics however exhibit relatively low voltage stress capability compared to polymer dielectrics, for example, 10 V/.mu.m for ceramic vs. 100 V/.mu.m (and as high as 400 V/.mu.m) for polymers. In addition, the energy density of a typical ceramic does not exceed about 0.1 J/cm.sup.3 (at 2 V/.mu.m), and is usually much lower, whereas polymer dielectrics can be operated as high as 2 J/cm.sup.3 (at 400 V/.mu.m).
The present invention gives ceramics the capability of operating at high temperatures with high voltage stress capability and high energy density, and gives polymers the capability of operating at higher temperatures than the present limit due to the presence of a liquid impregnant which must be used.